diff --git a/requirements.txt b/requirements.txt
index 787930e..40a1a1e 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1,3 +1,3 @@
 decorator==4.0.10
-lxml==3.7.2
+lxml==4.9.1
 networkx==1.11
diff --git a/requirements_py27_dev.txt b/requirements_py27_dev.txt
index 1a293f4..bb41702 100644
--- a/requirements_py27_dev.txt
+++ b/requirements_py27_dev.txt
@@ -37,7 +37,7 @@ jupyter-console==5.0.0
 jupyter-core==4.2.1
 lazy-object-proxy==1.2.2
 livereload==2.5.1
-lxml==3.7.2
+lxml==4.9.1
 MarkupSafe==0.23
 mccabe==0.6.0
 mistune==0.7.3
diff --git a/requirements_py3_dev.txt b/requirements_py3_dev.txt
index d1c99f0..b55ac33 100644
--- a/requirements_py3_dev.txt
+++ b/requirements_py3_dev.txt
@@ -34,7 +34,7 @@ jupyter-console==5.0.0
 jupyter-core==4.2.1
 lazy-object-proxy==1.2.2
 livereload==2.5.1
-lxml==3.7.2
+lxml==4.9.1
 MarkupSafe==0.23
 mccabe==0.6.0
 mistune==0.7.3